Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessObtain low-privileged Qsync Central account
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DeliveryReach network-exposed service
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ExploitSend unthrottled resource-allocating requests
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ExecutionExhaust shared resource
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ImpactDeny service to other users
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A06:2025 - Insecure Design
ASVS 5.0
V2 - Validation and Business Logic Resource allocation limits
MITRE ATT&CK
1 technique across 1 tactic: Impact The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Exploitation Conditions | Requires a valid Qsync Central user account (CVSS PR:L) with network reach to the Qsync Central service on a QNAP NAS; exploitation is remote and needs no user interaction (UI:N) once authenticated. The limiting factors that reduce real-world risk are: (1) the attacker must already possess or acquire credentials for a user account, so purely unauthenticated attackers cannot trigger it; (2) the impact is confined to availability (resource exhaustion / denial of service) with no data disclosure or modification; and (3) devices are only at risk if running an affected version prior to Qsync Central 5.0.0.1 and exposing the service to the attacker. No special non-default feature toggle is named in the advisory beyond having Qsync Central deployed. |
| Impact | This is a moderate, availability-only issue rather than a top-tier emergency. The vendor-supplied CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H, score 7.1) shows a network-reachable, low-complexity attack that requires an authenticated user account (PR:L) and yields no confidentiality or integrity impact - only high availability impact (resource exhaustion, consistent with CWE-770). All signals point the same direction and do not conflict: EPSS is low at 0.15% (36th percentile), the CVE is not on CISA KEV, and no public exploit was identified, so there is no public exploit identified at time of analysis. The combination of a required authenticated account plus a DoS-only outcome means this is a real but contained risk - a priority for internet-exposed, multi-user QNAP deployments where low-privileged accounts are common, but not a widespread-exploitation scenario. The main caveat is that the exact resource being exhausted and whether one user can deny service to others versus crashing the whole service is not specified in the description; treat the DoS blast radius as the key unknown to verify with QNAP advisory QSA-25-34. |
| Exploit ScenarioDerived | An attacker who already holds (or obtains) a low-privileged user account on a QNAP device running Qsync Central sends repeated requests over the network that cause Qsync Central to allocate a particular resource without limit. This exhausts that resource and prevents other legitimate users, systems, or processes from using the same Qsync Central functionality. No public exploit code is known, and the attack requires valid authentication (PR:L) over a network-reachable interface. |
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Alert meAnalysisAIv2 – Oct 18, 2026
Resource exhaustion in QNAP Qsync Central 4.x allows an authenticated remote user to consume service resources without effective throttling, potentially denying access to other users or processes on the NAS. Exploitation requires a valid Qsync Central account and network reach to the service; there is no confidentiality or integrity impact. QNAP has fixed the issue in Qsync Central 5.0.0.1 (2025/07/09), and no public exploit was identified at time of analysis (EPSS 0.15%).
Earlier versions of this analysis (1)
RemediationAI
Upgrade Qsync Central to 5.0.0.1 (2025/07/09) or later, as directed in QNAP advisory QSA-25-34 (https://www.qnap.com/en/security-advisory/qsa-25-34). If upgrading immediately is not possible, reduce exposure by restricting network access to the Qsync Central service to trusted networks or VPN, and review/disable unnecessary user accounts, since exploitation requires a valid account; these controls lower risk but restrict legitimate remote synchronization and do not remediate the underlying lack of throttling. Monitor NAS resource usage for abnormal consumption and enforce least-privilege account provisioning as an interim detection/mitigation measure, noting that monitoring adds operational overhead and is not a substitute for the vendor patch.
Affected VersionsENISA
Affects your stack
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Technical ContextAI · show details
Qsync Central is QNAP's file synchronization service for NAS devices. The flaw is CWE-770 (Allocation of Resources Without Limits or Throttling): the service does not adequately bound or throttle resource allocation for authenticated users, so a remote user with a valid account can exhaust a shared resource and degrade availability for other systems, applications, or processes. The affected CPE is cpe:2.3:a:qnap:qsync_central, covering 4.x versions before 5.0.0.1; the independent assessment maps this to CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H, reflecting a network-reachable, low-privilege, availability-only denial of service with no user interaction.
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- Exploit and PoC references, threat intelligence from 22 sources
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Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Network-reachable (AV:N) and low-complexity (AC:L) but requires an authenticated user account (PR:L); impact is availability-only resource exhaustion, so C:N/I:N/A:H and scope unchanged.
Primary rating from Vendor (qnapsecurity).
CVSS VectorVendor: qnapsecurity
Lifecycle Timeline
5DescriptionCVE.org
An allocation of resources without limits or throttling vulnerability has been reported to affect Qsync Central. If a remote attacker gains a user account, they can then exploit the vulnerability to prevent other systems, applications, or processes from accessing the same type of resource.
We have already fixed the vulnerability in the following version: Qsync Central 5.0.0.1 ( 2025/07/09 ) and later
Executive ViewAI
Organizations using An allocation of resources without limits or throttling vulnerability should be aware of notable risk from CVE-2025-33039 rated CVSS 6.5. Exploitation could compromise the security of affected deployments. Organizations should apply vendor updates when available and monitor for exploitation.
Apply vendor patch. If patching is delayed: restrict network access and enable monitoring.
Threat Intelligence Overview
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.
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EUVD-2025-32086
NVD
CVE.org
EPSS
GitHub PoC
Exploit-DB